1. Field of the Invention
The present invention relates in general to a molding device for molding a plastically moldable sheet, and more particularly, to a molding device of a type including lower and upper molds between and by which a plastically moldable sheet is pressed to form a shaped sheet member, such as a floor rug of a motor vehicle.
2. Description of the Prior Art
In order to clarify the task of the present invention, one conventional molding device of the above-mentioned type will be described with reference to FIGS. 11 and 12 of the accompanying drawings.
Referring to the drawings, there is shown a conventional molding device 100 which is designed to press a plastically moldable sheet 102 into a finished shaped sheet member, such as a floor rug of a motor vehicle. As is seen from FIG. 11, the molding device 100 comprises a stationary lower mold 104 and a movable upper mold 106. Each mold 104 or 106 installs therein a cooling device (not shown), such as a water flowing pipe or the like. The upper mold 106 is attached to a platen 108 of a hydraulic press (not shown). The lower mold 104 illustrated is formed with two elongate recesses 110 and 112 (each extending in a direction perpendicular to the surface on which FIG. 11 is carried) between and along which a ridge portion 114 extends, while, the upper mold 106 is formed with two ridge portions 116 and 118 (each extending in a direction perpendicular to the surface on which FIG. 11 is carried) between and along which an elongate recess 120 extends. That is, the work surfaces of the lower and upper molds 104 and 106 are so shaped or engraved as to match with each other. Due to the work of the hydraulic press, the upper mold 106 can be moved downward to press its engraved work surface against the counter work surface of the lower mold 104. Designated by numerals 104a and 106a are land areas provided by the lower and upper molds 104 and 106, which are mated with each other when the upper mold 106 is properly seated on the lower mold 104. The plastically moldable sheet 102 is of a sheet which comprises an upper layer 102a of cloth or the like and a lower layer 102b of thermoplastic impregnated felt or the like.
When molding of the plastically moldable sheet 102 is required, it is heated to a suitable temperature to be softened and then spread over between the lower and upper molds 104 and 106, respectively, as is seen from FIG. 11. For spreading the sheet 102, a spring-biased clamping device 122 is used by which laterally opposed sides of the sheet 102 are held and pulled outwardly as is shown by the arrows in FIG. 11. Then, the upper mold 106 is moved down and seated on the lower mold 104 to press the sheet 102 against the engraved work surface of the lower mold 104. Thereafter, the upper mold 106 is lifted to release the product, viz., the shaped sheet from the molding device 100.
However, as will be seen from FIG. 12, during the pressing work of the upper mold 106, the peripheral edge portions 116b and 118b of the ridges 116 and 118 of the upper mold 106 violently squeeze or press the sheet 102 against the outer walls of the recesses 110 and 112 of the lower mold 104 applying certain portions of the sheet 102 with considerable tension. This phenomenon sometimes induces formation of undesirable cracks at the tensioned portions of the sheet 102, particularly at the lower layer 102b of the same. Of course, such crack formation deteriorates the quality of the product.